1. Technical Field
The present invention relates in general to minimizing disruption of a marking particle image electrographically formed on a receiver member, and more particularly to active charging of a receiver member to substantially prevent disruption of the marking particle image thereon due to ionization of the air gap between the receiver member and a prefuser transport therefor.
2. Background Art
In reproduction apparatus, such as electrostatographic copiers or printers, for example, a uniformly charged dielectric member is exposed in an image-wise pattern to an image of original information to be reproduced. Such exposure of the dielectric member alters the uniform charge in a corresponding image-wise pattern forming a latent image charge pattern thereon. The charge pattern is then developed with pigmented marking particles from a development mechanism. The developed image is thereafter transferred to a receiver member, and fixed to the receiver member to form the desired reproduction of the original information.
In typical electrostatographic reproduction apparatus, transfer of the developed image from the dielectric member to the receiver member is accomplished by applying an electric field across the dielectric member and the receiver member while the two are brought into intimate relationship. The electric field is selected to attract the marking particles of the developed image from the dielectric member and hold the marking particles to the receiver member. When the receiver member is stripped from the dielectric member, the developed image remains with the receiver member. The receiver member is then transported to a downstream location where the marking particles of the developed image are fixed to the receiver member by application of heat and/or pressure for example.
It has been found that in electric field transfer, in order to obtain high transfer efficiency (i.e., to prevent any back transfer of the developed image marking particles from the receiver member back to the dielectric member), the electric field should provide an excess charge on the back side of the receiver member. As depicted in FIG. 2, when the receiver member (designated by the letter R) is delivered to the fixing location by a transport mechanism 136 made of grounded conductive material, charges Ca of opposite sign to the excess charges Cb on the back side Ra of the receiver member R build up on the surface 136a of the transport mechanism at the transport mechanism/receiver member interface.
It is now recognized that as the receiver member R moves along the surface 136a of the transport mechanism 136, the charges Ca on such surface flow toward the downstream edge 136b of the transport mechanism. Due to the fact that the flowing surface charges Ca cannot travel farther than the edge 136b of the transport mechanism, the charges collect at such edge. At the same time, due to the surface resistivity of the transported receiver member R, the charges on the back side Ra of the receiver member cannot move freely back along the receiver member in the direction toward the collection of opposite charge at the transport mechanism edge 136b. As a result, the transport mechanism surface charges Ca and the receiver member charges Cb separate, and the voltage therebetween increases until electrostatic breakdown (ionization) of the air occurs.
During such ionization, ions move to satisfy the respective charge imbalance at the transport mechanism edge 136b and the back side Ra of the receiver member R. The polarity of the ions moving to the back side of the receiver member is the same as the polarity of the charge on the marking particles P adhering to the front side Rb of the receiver member R. As a result of the forces between like polarity charges (i.e., since like polarity charges repel), some of the marking particles (only one such particle shown in FIG. 2, and designated by the letter P') of the developed image on the receiver member are forced in the downstream direction on the receiver member causing artifact-inducing image disruptions.
The severity of the image disruption depends greatly on the surface and volume conductivity of the receiver member, the environmental conditions, and the speed of the receiver member/transport mechanism separation. At a certain level, the disruption becomes obvious enough to cause the reproduction to be unacceptable to the user. In order to reduce the image disruption effects of ionization at separation of a receiver member from the transport mechanism, a passive static eliminator carbon brush may be utilized, or coatings or static dissipative paints may be applied to the surfaces of the transport mechanism. However, passive solutions are not totally effective in that their level of efficiency is of a fixed predetermined value, and they do not account for the variability in the amount of ionization for which there must be some accommodation.